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    <h1>
      Performance Tools
    </h1>
    <div class="subHeader"></div>

    <p><strong>Importing</strong></p>
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kr">import</span> <span class="nx">Perf</span> <span class="nx">from</span> <span class="s1">&#39;react-addons-perf&#39;</span> <span class="c1">// ES6</span>
<span class="kd">var</span> <span class="nx">Perf</span> <span class="o">=</span> <span class="nx">require</span><span class="p">(</span><span class="s1">&#39;react-addons-perf&#39;</span><span class="p">)</span> <span class="c1">// ES5 with npm</span>
<span class="kd">var</span> <span class="nx">Perf</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">addons</span><span class="p">.</span><span class="nx">Perf</span><span class="p">;</span> <span class="c1">// ES5 with react-with-addons.js</span>
</code></pre></div>
<h2>Overview</h2>

<p>React is usually quite fast out of the box. However, in situations where you need to squeeze every ounce of performance out of your app, it provides a <a href="/docs/react-component.html#shouldcomponentupdate">shouldComponentUpdate()</a> hook where you can add optimization hints to React&#39;s diff algorithm.</p>

<p>In addition to giving you an overview of your app&#39;s overall performance, <code>Perf</code> is a profiling tool that tells you exactly where you need to put these hooks.</p>

<p>See these articles for an introduction to React performance tooling:</p>

<ul>
<li><a href="https://medium.com/code-life/how-to-benchmark-react-components-the-quick-and-dirty-guide-f595baf1014c">&quot;How to Benchmark React Components&quot;</a></li>
<li><a href="http://benchling.engineering/performance-engineering-with-react/">&quot;Performance Engineering with React&quot;</a></li>
<li><a href="http://benchling.engineering/deep-dive-react-perf-debugging/">&quot;A Deep Dive into React Perf Debugging&quot;</a> </li>
</ul>

<h3>Development vs. Production Builds</h3>

<p>If you&#39;re benchmarking or seeing performance problems in your React apps, make sure you&#39;re testing with the <a href="/downloads.html">minified production build</a>. The development build includes extra warnings that are helpful when building your apps, but it is slower due to the extra bookkeeping it does.</p>

<p>However, the perf tools described on this page only work when using the development build of React. Therefore, the profiler only serves to indicate the <em>relatively</em> expensive parts of your app.</p>

<h3>Using Perf</h3>

<p>The <code>Perf</code> object can be used with React in development mode only. You should not include this bundle when building your app for production.</p>

<h4>Getting Measurements</h4>

<ul>
<li><a href="#start"><code>start()</code></a></li>
<li><a href="#stop"><code>stop()</code></a></li>
<li><a href="#getlastmeasurements"><code>getLastMeasurements()</code></a></li>
</ul>

<h4>Printing Results</h4>

<p>The following methods use the measurements returned by <a href="#getlastmeasurements"><code>Perf.getLastMeasurements()</code></a> to pretty-print the result.</p>

<ul>
<li><a href="#printinclusive"><code>printInclusive()</code></a></li>
<li><a href="#printexclusive"><code>printExclusive()</code></a></li>
<li><a href="#printwasted"><code>printWasted()</code></a></li>
<li><a href="#printoperations"><code>printOperations()</code></a></li>
<li><a href="#printdom"><code>printDOM()</code></a></li>
</ul>

<hr>

<h2>Reference</h2>

<h3><code>start()</code></h3>

<h3><code>stop()</code></h3>
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="nx">Perf</span><span class="p">.</span><span class="nx">start</span><span class="p">()</span>
<span class="c1">// ...</span>
<span class="nx">Perf</span><span class="p">.</span><span class="nx">stop</span><span class="p">()</span>
</code></pre></div>
<p>Start/stop the measurement. The React operations in-between are recorded for analyses below. Operations that took an insignificant amount of time are ignored.</p>

<p>After stopping, you will need <a href="#getlastmeasurements"><code>Perf.getLastMeasurements()</code></a> to get the measurements.</p>

<hr>

<h3><code>getLastMeasurements()</code></h3>
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="nx">Perf</span><span class="p">.</span><span class="nx">getLastMeasurements</span><span class="p">()</span>
</code></pre></div>
<p>Get the opaque data structure describing measurements from the last start-stop session. You can save it and pass it to the other print methods in <a href="#printing-results"><code>Perf</code></a> to analyze past measurements.</p>

<blockquote>
<p>Note</p>

<p>Don&#39;t rely on the exact format of the return value because it may change in minor releases. We will update the documentation if the return value format becomes a supported part of the public API.</p>
</blockquote>

<hr>

<h3><code>printInclusive()</code></h3>
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="nx">Perf</span><span class="p">.</span><span class="nx">printInclusive</span><span class="p">(</span><span class="nx">measurements</span><span class="p">)</span>
</code></pre></div>
<p>Prints the overall time taken. If no argument&#39;s passed, defaults to all the measurements from the last recording. This prints a nicely formatted table in the console, like so:</p>

<p><img src="/img/docs/perf-inclusive.png" alt=""></p>

<hr>

<h3><code>printExclusive()</code></h3>
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="nx">Perf</span><span class="p">.</span><span class="nx">printExclusive</span><span class="p">(</span><span class="nx">measurements</span><span class="p">)</span>
</code></pre></div>
<p>&quot;Exclusive&quot; times don&#39;t include the times taken to mount the components: processing props, calling <code>componentWillMount</code> and <code>componentDidMount</code>, etc.</p>

<p><img src="/img/docs/perf-exclusive.png" alt=""></p>

<hr>

<h3><code>printWasted()</code></h3>
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="nx">Perf</span><span class="p">.</span><span class="nx">printWasted</span><span class="p">(</span><span class="nx">measurements</span><span class="p">)</span>
</code></pre></div>
<p><strong>The most useful part of the profiler</strong>.</p>

<p>&quot;Wasted&quot; time is spent on components that didn&#39;t actually render anything, e.g. the render stayed the same, so the DOM wasn&#39;t touched.</p>

<p><img src="/img/docs/perf-wasted.png" alt=""></p>

<hr>

<h3><code>printOperations()</code></h3>
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="nx">Perf</span><span class="p">.</span><span class="nx">printOperations</span><span class="p">(</span><span class="nx">measurements</span><span class="p">)</span>
</code></pre></div>
<p>Prints the underlying DOM manipulations, e.g. &quot;set innerHTML&quot; and &quot;remove&quot;.</p>

<p><img src="/img/docs/perf-dom.png" alt=""></p>

<hr>

<h3><code>printDOM()</code></h3>
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="nx">Perf</span><span class="p">.</span><span class="nx">printDOM</span><span class="p">(</span><span class="nx">measurements</span><span class="p">)</span>
</code></pre></div>
<p>This method has been renamed to <a href="#printoperations"><code>printOperations()</code></a>. Currently <code>printDOM()</code> still exists as an alias but it prints a deprecation warning and will eventually be removed.</p>


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